Technical Abstract:
Field studies have shown that augmentative releases of parasitoid wasps into bins of stored wheat can suppress populations of the lesser grain borer by 90% compared to control bins. Insect fragments from flour samples milled from bins treated with parasitoids were reduced by 89% and the number of insect damaged kernels was reduced by 92%. Combining biological control with aeration can have synergistic effects that can result in higher levels of population suppression. Laboratory studies with the lesser grain borer, Rhyzopertha dominica, showed that the parasitic wasps that attack larvae of this beetle were ten times more effective when the grain was cooled with aeration from 32ºC to 25ºC. These hymenoptera parasitoids frequently occur naturally in stored grain. Grain sampling can determine if natural enemies are present, or if the storage would benefit from augmentative releases. There are many factors that impact the success of a biological control program, such as releasing the appropriate species, number of parasitoids to release, and timing the releases to coincide with the susceptible host stage. The overlying strategy for a low-risk control program is prevention. Environmental conditions need to be selected that will limit the pest insect’s ability to develop and reproduce in the grain. In addition, these methods need to be neutral, or favor the growth and development of natural enemies.